[Aurornis]

The video quality degrades at longer distances. You can't get the full bandwidth at the maximum distance, but you might see enough to navigate.

Communicating with a drone up in the sky is easier than something like your WiFi or your cell phone because you have a nice, clear line of sight to the drone. Fly behind a hill, building, or some trees at distance and the drone will lose connection and go into safety mode.

The free space path loss at 20kM is 126dB at 2.4GHz in perfect conditions, or 134dB at 5.8GHz. If you start with the 1 Watt nominally allowed by regulations, that's +30dBm. Subtract 126dB and you're left with -96dBm. That's a weak signal, but it's actually close to the receive sensitivity of the WiFi card in your laptop, believe it or not. I would guess the DJI gear uses narrower channels than WiFi to achieve a better noise floor than the 20MHz (or wider) channels you get with WiFi.

The 20km figure is really an extreme upper limit. Realistically you'd probably need a high-gain antenna pointed in the direction of the drone to achieve it.

[palata]

That's super interesting! Would you have resources to recommend to learn about that?

For instance: where do you get that "the free space path loss at 20kM is 126dB at 2.4GHz in perfect conditions, or 134dB at 5.8GHz"? And why does 1 Watt translate to +30dBm?

[magnat]

https://www.antenna-theory.com/ is a good starter for apprentice-level RF voodoo.

30 dBm = 30 decibels wrt to 1 milliwatt. 10 decibels = 1 bel = 10-fold increase of the base quantity, so 30 decibels = 10 x 10 x 10 = 1000x increase, so 30 dBm = 1000x 1 mW = 1 W.

[palata]

Oh nice, thanks!

[pseudosavant]

I don't know enough to offer any real sources, but I'll share that I've found ChatGPT very useful for learning stuff like this - really solidly documented and established science/engineering.

I asked* "When making a wireless transmission what is the signal loss at 20km for 2.4Ghz?" and it gave an excellent explanation of free space path loss, stepped through the calculations, and gave the correct answer.

I've had it explain various kinds of first-order filters, especially for electric guitar circuits too. And asking follow up questions works well with how my brain works.

*Link in case you are curious: https://chat.openai.com/share/d0fcf90e-9d2e-4078-9bb4-60717f...

[palata]

> but I'll share that I've found ChatGPT very useful for learning stuff like this

I get your point, but no way I use ChatGPT. Other than all the ideological issues I have with it, I just can't trust it.

> and gave the correct answer.

Are you saying that because you believe it did, or because you already knew the answer? I don't trust ChatGPT, so I don't want to learn anything it says. And I don't need it for stuff I already know.

[TheHappyOddish]

It's not that different to Wikipdia. Trust, but verify. It's usually correct, but regardless it's a useful starting point for a topic.

[palata]

Wikipedia shows sources, does not hallucinate, and shows the same content to all the users (meaning that if there is a mistake, someone else can actually report it).

That is very different to me.

[TheHappyOddish]

Those are accurate details, but if you zoom out they're still contextually very similar - a swathe of text on a subject written by someone (or something) you have no veritable trust in but is usually fairly accurate.

You should independently fact check either source. Wikipedia is slightly easier, but after you have a base subject matter understanding you should have the terminology to validate anyway.

I suspect you just don't like it, which is perfectly fine.

[pseudosavant]

Because there are other ways (simple Google search, asking an EE friend, etc) of validating the answer. Often I'm looking to learn a concept so it isn't like I'm using it to solve a bunch of things. Just validate my learning. It is easily as good as having one of my EE friends explain the concept to me.

[okdood64]

Cool stuff.

I suspect military communications uses wattage MUCH stronger than what's allowed by regulation in the battle space, correct?

[exar0815]

Lower Frequencies, More power, more directionality, more digital signal Processing are the four ways to increase range.

Each has their own disadvantages and advantages, so it's always a tradeoff.

[regularfry]

The channels can't be too narrow bandwidth and still fit any sort of 1080p video feed in them. If I'm remembering my signals courses right, raw 1080p at 60fps would need something like 6GHz, so even at 100:1 compression they'd still need 60MHz channels.